Modern-day construction cranes, such as telescoping boom cranes, like all heavy equipment, are designed with safety in mind, and great care is exercised to provide all necessary safety devices including signal devices to alert the crane operator to an approaching or existing safety hazard during the operation of the crane. Despite strenuous efforts to provide the best safety features on cranes and other construction machinery, there are always some accidents and after the occurence of such accidents efforts are renewed to prevent the accident from recurring.
The present invention relates to a safety device or arrangement for cranes which is intended to deal with one particular potential hazard which could result in a serious accident even though the likelihood of such an accident is remote. In telescoping boom cranes of a certain type, the boom fly section is extended from the next interior section by an extension cable reeved over pulley means on the next interior boom section and positively anchored to a further interior boom section, such as the boom base section. This fly section extension cable actually bears the load which is being carried by the boom and should the extension cable part or fail at any point the fly section would retract with the load out of control, possibly resulting in a very serious accident.
This invention seeks to provide an extremely simple fail-safe arrangement in the form of a safety stop device having components on the extension cable and on the boom fly section which come into positive contact substantially instantly in the event of failure of the extension cable to prevent the retraction of the loaded fly section without control. The arrangement is compact, extremely strong and adds very little to the cost of the equipment while greatly enhancing its safety, and does not interfere with normal operations of the boom or require any significant modification of the conventional construction of the boom.
Various detailed features of the invention will be apparent during the course of the following description.